“Common signs of vitamin C intolerance include redness, itching, stinging, or a burning sensation upon application,” explains board-certified dermatologist Ife J. Rodney, M.D., founder of Eternal Dermatology. “Less recognized signs could include small bumps, hives, or worsening of existing skin conditions like eczema or rosacea.” 

Some people (like me) can even experience breakouts—in fact, acne was the only symptom I had, which made it difficult to pinpoint what, exactly, was causing this inflammation. I had some suspicions, so I eliminated every potentially-irritating active in my routine, save for the vitamin C. Lo and behold, I had found the culprit. 

I suggest committing to a similar “elimination routine” if you think you might be dealing with a sensitivity. Or, as Rodney suggests, you can try a patch test: Apply a small dot of product daily near your ear or underside of your arm, then monitor it for a few days for any changes. Of course, you can also consult a dermatologist for a more personalized read. 

OK, but here’s the thing: Vitamin C comes in many derivatives, ranging in stability. L-ascorbic acid is the most potent (and unstable) form of the antioxidant, and it’s this type that causes the most sensitivities. Other forms include magnesium ascorbyl phosphate, tetrahexyldecyl (THD) ascorbate, ascorbyl palmitate, sodium ascorbyl phosphate, and ascorbyl tetraisopalmitate.

Both ascorbyl-6-palmitate and magnesium ascorbyl phosphate are stable at neutral pH, which may make them gentler on the skin. Similarly, “THD ascorbate is less irritating, more stable, and can easily be used in oil-based products,” notes board-certified dermatologist Hadley King, M.D. (Feel free to brush up on your vitamin C knowledge here.)